Wayward FIL has sent me a very humble email in which he attempts to reconcile what his son, WH, has done and begin to answer my Q about why he didn't see WH when he was a kid growing up.
Writes that he is devastated by the news of WH leaving me pregnant. Says the news has shattered the illusion he has held for 40 years that abandoning WH was morally conscionable.
Says that although now he feels in no position to justify himself, he left MIL and WH because relations with MIL were hateful, and wanted another man to step in and fill his shoes as WH's father fast*.
Also said he thought MIL would have demonised him, which he found out later, was not the case but it was too late by then to make up lost time with WH who was by then an adult.
* my WH said to me I should find a step-father for the child - the quicker the better.